The main approaches to reduce the flammability of polyamides are melt additives, topical finish treatments, and copolymerization with flame resistant monomers. Melt additives generally include halogenated organic compounds with high levels of bromine or chlorine. A second component when halogenated compounds are employed is antimony trioxide (Sb.sub.2 O.sub.3). Other popular elements found in melt additives are phosphorus and molybdenum. Finish treatments generally require high add-on levels, and many of these lack the durability to cleaning procedures required for polyamide fabrics such as mattress ticking, apparel, upholstery and drapery.
Phosphorus compounds are widely used to reduce the flammability of thermoplastic polymers. For example U.S. Pat. Nos. 3,987,008; 4,203,888; and 4,940,772 disclose a broad variety of organic phosphor compounds in thermoplastic polyester.
U.S. Pat. No. 3,987,008 discloses a polyphosphonate with arylene and haloarylene groups. U.S. Pat. No. 4,203,888 discloses an aryl diphosphate.
One disadvantage of these phosphorus compounds is that they are inert additives which build a separate phase in the thermoplastic polymers with negative influence of the fiber properties like poor dyeability.
U.S. Pat. No. 4,940,772 describes a process for producing a flame resistant polyester by copolymerizing a polyester with an unsaturated compound and reacting this copolyester with a specific phosphorus compound.
An object of the present invention was to provide polyamide fibers with reduced flammability and simultaneous excellent physical fiber properties. Another object was to improve heat stability and dyeability of the fibers. Another object was to provide a method for producing polyamide fibers with reduced flammability.
Still another object was to provide a masterbatch of polyamide with reduced flammability for the production of polyamide fibers by melt mixing and melt spinning.